1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a method of routing calls in third generation Internet Protocol (3G.IP) networks.
2. Description of Related Art
In second generation. (2G) circuit-switched networks today, calls to a mobile subscriber roaming in a visited network are forced by the characteristics of 2G networks to follow a voice transmission path which is not efficient. Calls to the mobile subscriber must be delivered first to the subscriber""s home network, and then to the visited network, regardless of where the subscriber is roaming. This procedure can sometimes lead to very inefficient call routing.
For example, if a subscriber from Montreal roams to Dallas, and someone in Dallas calls him utilizing his Montreal telephone number, the call is routed to the subscriber""s home network in Montreal and then back to the subscriber in Dallas. This occurs because number analysis in the caller""s switch in Dallas recognizes the 514 prefix for Montreal, and directs the switch to deliver the call as a Public Switched Telephone Network (PSTN) call towards Montreal. The call is received in Montreal by a Gateway Mobile Switching Center (G-MSC) that interrogates the Montreal Home Location Register (HLR) and gets back a routing number such as a Temporary Location Directory Number (TLDN) allocated by the Dallas MSC currently serving the roamer. Finally, the G-MSC routes the call back to Dallas based on the TLDN analysis. The result of this routing is that instead of being routed as a local Dallas call, the call involves two long-distance trunks between Dallas and Montreal.
As noted above, there are characteristics (or constraints) of the 2G networks which force the call to follow an inefficient voice transmission path. The first constraint is related to the circuit-switched transport of the voice information and signaling. A voice trunk is seized between the caller and the called party, and remains dedicated to carrying the voice information for the duration of the call. The call control signaling, even though it does not follow the same physical path as the voice, is also bound to the configuration of the circuit-switched network. For example, even though the Integrated Services User Part/Signaling System 7 (ISUP/SS7) signaling is delivered over the SS7 signaling infrastructure rather than the voice trunk, the signaling still has to reach the same switch where the voice trunk terminates. For example, if a call between Subscriber-A and Subscriber-B must cross a transit switch because of a particular circuit-switched configuration, then the ISUP/SS7 signaling must also cross the same transit switch.
The second constraint of 2G networks that causes inefficient routing is the North American number allocation process which does not make a distinction between landline and wireless subscribers. Because of this, in order to keep the switch routing tables throughout the network at a manageable size, the distinction between a landline subscriber and a wireless subscriber is made only in the home network of each particular subscriber. The G-MSC function discriminates a wireless subscriber number from a landline number and performs the HLR interrogation. Therefore the G-MSC functionality must always be performed in the home network.
This routing procedure has also been proposed for third generation all IP (3G.IP) networks. The introduction of 3G.IP networks will make one of the constraints disappear: the new 3G networks will replace the circuit-switched infrastructure with packet switched technology providing multiple connectionless transmission paths between the origin and the destination points. The subscriber number allocation constraint, however, is maintained. So even in 3G.IP networks, the subscriber""s home network will be the only one that knows where the subscriber is roaming and what services are activated for the subscriber.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a method of efficiently routing calls in 3G.IP networks which, while continuing to perform the location interrogation by a Gateway functionality located in the home network, chooses an optimal path for the payload transport. The present invention provides such a method.
The present invention is an improved call routing method applicable to 3G.IP subscribers capable of performing voice and/or video calls, and requesting real-time characteristics such as multimedia sessions. For doing so, the subscriber makes use of the H.323 signaling protocol from the International Telecommunications Union (ITU) or the Session Initiation Protocol (SIP) signaling protocol from the Internet Engineering Task Force (IETF). The call routing method of the present invention enables 3G.IP network infrastructures to choose an optimal path for the payload transport while continuing to perform the location interrogation by a Gateway functionality located in the home network.
Thus, the present invention is a method in a 3G.IP network of routing a call from an originating subscriber in an originating network to a mobile terminating subscriber roaming in a visited network, the mobile terminating subscriber having a home network that maintains location information for the mobile terminating subscriber. The method begins when the originating subscriber sends a call origination message to a gatekeeper in the originating network. The gatekeeper then obtains from the home network, location information for the mobile terminating subscriber in the visited network. This is followed by sending an IP address for a node in the visited network to the originating network, and routing the call directly from the originating network to the visited network.